1) Field
Embodiments of the present invention pertain to the field of plasma processing equipment and, in particular, to plasma resistant coatings for components of a plasma processing chamber.
2) Description of Related Art
Vacuum plasma processing chambers are used for plasma processing during fabrication of devices, such as photovoltaics and integrated circuits. Process gases are flowed into the processing chamber while a field is applied to the process gases to generate a plasma of the process gases. To reduce operating costs, the lifetimes of the components within a plasma processing chamber exposed to the processing plasma are extended by designing the components to be plasma resistant. As used herein, the term “plasma resistant” refers to a resistance to erosion and corrosion when exposed to the plasma processing conditions generated within the plasma processing chamber. Plasma resistant components are currently formed out of bulk materials or by thermal spraying a protective coating over a substrate.
FIG. 1 depicts a conventional thermal spraying method 100 employing a plasma, commonly referred to as plasma spraying. The feedstock material 101, usually in the form of a powder, liquid or wire, is introduced into a high temperature plasma torch 105. A feed gas 120 (e.g., argon, nitrogen, hydrogen, helium) flows around a cathode 122 toward an anodic nozzle 123. A plasma is initiated by a high voltage discharge, which causes localized ionization and a conductive path for an electrical arc to form between the cathode 122 and the anodic nozzle 123, thereby forming a plasma discharge of the feed gas 120. The plasma exits the anodic nozzle 123 as a plasma torch 105 which does not carry electric current (i.e., a neutral plasma). The temperature of the plasma torch is on the order of 10,000K, melting or softening the feedstock material 101 into droplets 107 and propelling them towards the substrate 110.
The molten droplets 107 flatten upon impinging the substrate 110 and rapidly solidify to form a coating 115 consisting of pancake-like lamellae commonly referred to as “splats.” As the feedstock particles usually have sizes from a few micrometers (μm) to more than 100 μm, one lamella typically has a thickness of about 1 μm and lateral dimension from several to more than 100 μm. Between individual lamella, there are small voids, such as pores, cracks and regions of incomplete bonding.